Plastic injection machine



June 4, 1963 E. D. TRUEBLOOD PLASTIC INJECTION MACHINE 3 Sheets-Sheet l Filed Dec. 22, 1960 MMI/M924? ATTORNEYS June 4, 1963 E. D. TRUEBLOOD 3,091,809 PLASTIC INJECTION MACHINE Filed Dec. 22, 1960 FIG-2 3 Sheets-Sheet 2 IN VEN TOR. ELMER D. TRUEBLOOD ATTORNEYS June 4, 1963 E. D. TRuEBLooD 3,091,809

PLSTIC INJECTION MACHINE Filed Dec. 22, 1960 5 Sheets-Sheet 3 LEFT KNocK-ouT RIGHT I NocI ouT 7, MoToR 7o f MoToR To FIG -3 ^7z 7o -7s Tof LEFT PINS, uP RIGHT PINS, uP

HOLD-DOWN 80 m HOLD-DOWN /80 [l0 s "L y soL. soL. T" I.. l

los@ los/I I TESL-Ac START"z .E 86a PINSDOWN i 'zo 82a TABLE L. 87a I TABLE R. 'ab 'zo I B2b 83a I/Sa I I I 6I: 8 g-IIS I TABLE R. PINS uP-* I "5b 87| m' I6 y- IE 1 -IL KL F|G 4 '21a Wzof. lzl@ /zI FuNc'rIoN SELECTOR SwITcI-I-IIS Up UP-DO (HALF) OFF (FULL) Q RELAYCOIL O a 0 i I-l, f` INVENTOR. "5a :Fr F -II-N-O RELAY I 0 CONTACTS ELMER D.TRuEBLooD :l: ,HLNS BY ld-r n o o o MMM? ATTORNEYS for visually gauging the United States Patent O 3,091,809 PLASTIC INJECTIN MACHINE Elmer D. Trueblood, Dayton, Ohio, assignmto Trueblood, Inc., Dayton, Ohio, a corporation of Ghio Filed Dec. 22, 1960, Ser. No. 77,629 2 Claims. (Cl. 18-30) This invention relates to plastic injection machines, and more particularly to such a machine including mechanism for the automatic ejection of a formed article.

The invention has particular applicability to plastic machines in which two or more bottom mold members are serially moved between injection and ejection stations lalthough various features of this invention may be applied to an injection machine hav-ing a mold comprised of a single top and bottom mold member.

The apparatus of lthis invention provides automatic, accurate, :and consistent ejection of a molded article from one half of a mold. The invention preferably includes provision for the regulation of the height of the ejecting movement of knock-out pins, and Ia scale is provided extent of movement between full up and full down of the pins. Preferably, the invention provides for the selection of two modes of operation consisting of pin stripping movement and retention in the ejecting position, and the fully automatic extension and return pin stripping movement.

The preferred embodiment of this invention is shown as applied to a plastic machine which includes a Imovable table upon which a pair of bottom mold members are supported for respective movement into an. injecting position, or station, immediately under an upper cooperating mold member, and one of a pair of ejecting stations positioned adjacent the opposite end of the bed.

The ejecting mechanism at each ejecting station includes a uid piston motor which is arranged to effect the ejection of the article formed and carried within the mold member, by the reciprocation of knock-out pins. A common control circuit is provided for ejecting the mechanism at each of the ejecting stations. This control circuit includes limit switches at the ends of the table movement which determine the position of the table on the bed. The control further includes an adjustable limit switch arrangement by means of which the upward eX- tent of knock-out movement of the knock-out pins is controlled and by means of which fthe ejecting movement may be adjusted, as desired. A scale adjacent the knockout limit switch provides a convenient guide for adjustment.

This invention eliminates the mechanical cam-operated workpiece ejectors which are commonly employed in plastic injection machines and which are not readily subject to control of height or mode of operation.

It is therefore an object of this invention to provide a plastic machine as outlined above having a workpiece ejector -including Ia uid motor.

A further object of this invention is the provision of a plastic machine Ias outlined labove having a fluid knockout motor with provision for adjusting the height or eX` tent of knock-out movement.

Another object of this invention is Ato provide an automatic workpiece ejector for plastic injection machines which have a plurality of bottom mold members movable into ejecting stations.

A still funther object of this invention is the provision of a molded article ejector mechanism including the selection between fully automatic ejection and retraction or ejection and hold movement of the ejecting pins.

A still further object of this invention is to provide a mechanism as outlined above which is particularly adapted for use in plastic injection machines wherein a plurality of lower mold members are moved in succession into one or more ejecting stations for .the automat-ic ejection of the molded article at each such station.

Other objects and advantages of the invention will be apparent from the following description, the accompanying Adrawings and the appended claims.

In the drawings:

FIG. l is a front elevational view of a plastic machine constructed according to this invention;

FIG. 2 is an end elevational view of the machine of FIG. l, partly in section, taken generally along the line 2 2 of FIG. 1;

FIG. 3 is an electrical and FIG. 4 is a diagram of some of used in FIG. 3.

Referring to the drawings, which illustrate `a preferred embodiment of .this invention, a plastic injection machine constructed according to this invention is illustrated in FIGS. l and 2 as including a bed having a base plate li). A shuttle table guide l2 is mounted on the bed 10` and -is forme-d with a flat upper surface 13 upon which a shuttle table 15 is slidably mounted. The `table 15 is retained on the table guide l2 by means of gibs 17 and 18 (FIG. 2) positioned respectively along the outer and inner lower edges of the guide l2 for engagement with ledge por-tions 19 formed on the table guide 12, aS is well-known and understood in the art.

'Dh-e shuttle table 15 is movable on the guide in sequence between two `extreme positions by a `double-acting hydraulic cylinder 20. The limits of movement of the table 1S may be accurately controlled by a pair of oppositely disposed butt screws 23 Iand 24 which are respectively mounted in uprights 25 and 26 attached to the guide 12 for engagement with the ends of the table 15. t

Injection machines of the type thus far described normally include a vertically movable head (not shown) mounted between the upright supports 28 and 29 within which is carried "a top mold member 3d. Preferably, a pair of spaced apart lower or bottom mold members 32 and 33 are mounted for movement with the table l5 in `such 4a manner that one of the bottom mold members is in alignment with the upper member while the other bottom mold member is positioned at an ejection station adjacent one of the ends of the shuttletable guide 12. Thus, one of the lower mold members may be injected by a nozzle 35 while the other lower mold member is positioned for stripping an arti-cle previously formed therein.

It -may be seen lin FIG. 2 that this invention is applied to the universal type of molds for plastic injection wherein the upper mold member 30 is formed with a top universal mold shoe 4d and a top sub-shoe 41. The sub- -shoe 411 forms a removable insert within the shoe 40. The top shoe also includes one half 43 of a nozzle diagram of the control circuit;

the electrical symbols plate.

Each of the cooperating bottom mold members is formed with a bottom mold shoe lwhich may be generally H-shaped in vertical section, as shown, to provide Ia recess to receive a bottom mold sub-shoe 46. The mold shoe 45 also supports a cooperating nozzle plate 47. The sub-shoes 4l and 46 respectively form a cavity within which an article v52 is formed by injection plastic molding.

The lower mold members 32 and 33 are preferably identical in their mechanical arrangement and form, and each include ejeetinfg means for the removal of the molded Aarticle 52 in order to clear the mold and to make it ready for a subsequent molding operation. This ejecting means may consist of one or more ejector pins 55 which are positioned for vertical reciprocal movement within the shoe 45 and sub-shoe 46. The number of pins 55 and their location are dictated by the nature of the article being formed, and in the illustrated embodiment, two pins V55 are employed to engage the extending :electrical terminals of a molded electrical plug forming the larticle 52. The ejecting means in each of the lower mold members further includes a stripper plate 58 upon 'which Ithe lower ends of the pins 55 rest, and which is movable within the cavity 59 formed in the shoe 45 to eifect ejecting movement of the pins 5S.' Suitable guide pins or other guide means may be formed on the plate, or provided to cooperate with the plate 58 to assure that it moves vertically without binding or placing a strain upon the ejector pins 55.

The invention includes knock-out means lfor operating the stripper plate S3 to strip the molds at each of the Vejeoting stations. 'In the following description, the knockout mechanism at one of the stations is described in detail, and it is understood that the mechanical arrangements of the other ejecting stations may 4be identical in form. Referring to FIG. 2, an ejector plate operating member includes a pair of knock-out pins 6h' and 61 which are mounted for reciprocal vertical movement in the 4bed 10 and the guide 12 adjacent one end of the guide. As clearly shown in FlG. l, a major portion of each of the pins 60 and 61 is mounted in suitable openings formed in the table guide portion 12 of the bed and the =bed base plate 1G providing for guided raising and lowering movement rof the pins therethrough. The knock-out pins 66 and 61 are movable between a llowered or retraoted position where they clear the table 115 to a raised ejecting position extending through the table. lThus, the table 15 'is formed with suitable openings 64 and 65 which move into registering alignment respectively with 'the pins 60 `and y61 when the lower rnold member 32 is in the ejeoting .station at the left-hand end of the guide .12.

Operating and mounting means for the knock-out pins 60 and `61 includes a knock-out plate 68 upon which the lower ends of the pin-s may :be secured for vertical movement, and a two-way fluid motor 71?/ having a piston rod 71 connected to the plate 68 to erect vertical movement thereof.

The motor '70 is preferably of the hydraulic piston type, although it is within the `scope of this invention to employ an air motor, or other types of positive displacement iluid motors, for this purpose. Also, the motor 79 is preferably of the double-acting type includ- .ing a pair of opposite inlets 72 and 73 through which uid under pressure may be admitted to control the eX- tending and retracting movement of the piston rod 71.

The ejecting movement of the motor '70, and therefore the movement of the pins 6% and 61, is controlled by a three-position, double solenoid, spring-centered valve 80 connected to apply pressure to the inlets 72 and 73. The valve Si) may be operated to eifect either extending lor retracting movement of the rod 71, or may be centered to hol-d the rod in any predetermined position. The solenoid coil portions .of the valve 8) `form a part of a control circuit, shown 'in detail in FIG. 3. Also, left and right limit switches 82 and 83 (YFIG. 1) are arranged to be actuated by the movement of the table d in either of its opposite limit positions. The table I is preferably provided with separate adjustable push lrods 84 and 85- yat the opposite ends thereof by means of which the limit switches 83 and 82 are actuated. The purpose of the limit switches is to con-trol the operation of the associated ejector mechanism according to which end of the bed a lower mold member 32 or 33 is positioned for stripping.

The electrical control circuit of FIG. 3 further includes a pair of knock-out limit switches S6 and 87, one each being mounted on opposite sides `of the machine. Referring lto FIG. 2, the limit switch 86 is seen as including an actuating arm 88 which is extended for operation by the movement of the knock-out plate 68. the plate `68 includes an arm-like extension 96 upon which is mounted a threaded rod 91. Adjustable top and Specifically,

bottom nuts `93 and 94 are threaded onto the rod 91 and receive the arm S8 therebetween for operating the switch '85. Lock nuts 95 and 96 retain a given adjustment of the nuts 93 land 94. -A knock-out adjustment scale is lalso attached to the arm 90 and forms the means by which the movement of the knock-out pins 60 and 61 may be visually gauged according to the adjustment of `the nuts 93 and 94.

FEhe diagram of FIG. 3 shows the hydraulic and electrical circuit components and their connection for the control of ejector mechanisms at the ejecting stations on the plastic machine of FIGS. l and 2. However, this invention is not limited to the particular electrical or hydraulic circuit described, nor is it limited to plastic machines having a shuttle table, and the principles of this invention may be applied to a rotary table wherein a plurality of bottom mold members move serially past injection and ejection stations. Further, the principles of this invention may be applied to apparatus for the ejection of molded parts from a single top or mold member.

In the diagram of FIG. 3, the hydraulic arrangement for the left knock-out cylinder motor 70 is shown. The knock-out cylinder motor for the ejecting mechanism on the opposite end of the table is designated as 70'. Similarly, the control valve for the motor 70' is designated as S0', corresponding to the control valve 80. The motors 70 and 70 are operated respectively through the valves 30 and Sli' from a source of hydraulic pressure including a tank and a pump 106, which may, for convenience, consist of the central hydraulic supply for the injection machine.

The valves 80 and 80 are normally centered in their neutral position, as shown, and in this position, the inlets 72 and 73 of the associated cylinder motor 70 or 70 Vare blocked, and the pump 106 is by-passed to the tank 105. Thus, the pins 60 and 61 are normally held in a given position which may be either the retracted position or an extended position of adjustable height. The valves 80 and 86 each include operating solenoids 110 and 111 which are eiective respectively to cause the eX- tensicn and retraction of the connected knock-out pins.

The electrical portion of the circuit of FIG. 3 is one which has been found suitable for the control of the valves 80 and 80', and includes a start button 112 by means of which an operator may initiate the movement of the ltable 15 into its opposite positions through the shifting of the table by the cylinder motor 21. The start button includes one make and two break sets of contacts. The circuit also includes a function selector switch which may be positioned with the start button 112 and the other controls of the injection machine on a control panel convenient to the operator.

The positions of the function selector switch 115 are illustrated in FIG. 4, where it is seen that this switch is of the double-pole, double-throw type with a neutral off position. The function switch l115 has contacts connected to the knock-out limit switches S6 and 87 so that an operator can select either a half cycle of operation wherein the knock-out pins 69 and 6-1 are moved to the raised position and are held there, or he may lselect la full Vcycle of operation wherein the pins are raised to effect ejection of an article 52 and then are immediately lowered.

The circuit of FIG. 3 further includes a pair of relay coils and 121. The associated relay contacts are designated by 12Go, 121er, etc. Further, by way of explanation, the left and right limit switches 82 and 83 are each double-pole, single-throw 'switches which are normally open, but are closed when contacted by theV pins 84 land 85, and their contacts are similarly designated by the suiiixes a and b.in the manner of relay contacts. Similarly, the knock-out limit switch 86 at the left side of the table and the limit switch 87 at the right side have contacts designated with the sutiixes a and b. For the purpose of illustration', the electrical circuit is shown with the table 15 in the full left position and with Ithe pins down.

To initiate a sequence of operation, an operator depresses the start button 112. This causes -the holding relay 121 to drop out due to the breaking of the circuit to its holding contacts 121a. The start button 112 also causes the table to shift to its opposite position by the motor 120 through the usual table shifting circuit designated at 130 and the closed contacts 86a and 87m -It is assumed that the table 15 is now shifted to the left-hand position. Upon the release of the start button 112', the relay 120 is energized just as soon as the table moves into `the left position by the closing of switch contacts 82a.

Relay 12) operates to apply power through relay contacts 120a to the upper half 115a of the function selector switch 115. In either position of the switch 115, power is applied .through the normally closed contacts 12112 and the closed limit switch contact S2b to the up solenoid 110 of the valve 80 which causes `an ejecting stroke of the motor 70.

The article 52 is thus ejected by the upward movement of the knock-out pins 60 and 61, which movement is translated by these pins to the stripper plate 58- and the ejecting pins 55. When the pins 55 arrive at an upper limit position as determined by the setting of the knock-out adjusting nut 94, the arm titiy of the switch $6 is tripped overcenter. The closing of the contacts 86h energizes the holding relay 121 which operates to remove the power from the solenoid 110, thus permitting the valve 34) to center land stopping the ejecting movement of the motor 30 at a point determined by the setting of the nut 94. Relay 121 loclcs in through its holding contact 121a and will not be `released until the start button 112 is pushed to initiate a new cycle of operation.

Assuming that the =function -selector switch 115 is in the up position, the ejector pins will be held in the raised position until the start button 112 is depressed again -to drop out the holding relay 1-2'1. The button 112 also 4releases relay 120 which therefore permits the solenoid 111 to be energized through the normally closed relay contacts 120e and 121C. The table 15 is interlocked and prevented from shifting until both of the switch contacts 86a land 87a are closed, Iindicating that the knock-out pins 6i) and 61 are in the fully retracted position clear of the openings 64 and 65.

If the function selector switch 115 is set in the updown position, the closing of the contacts 86b of the knock-out limit switch 86 when the pins Areach their predetermined lupward movement immediately effects the energization of the :solenoid 111 to retract the pins through the switch contacts 115b. Thus, the operator is free to remove the loosened article 52 from the lower mold member 32 or 33, and to reload the mold at the ejecting station where it is in the open and clear of the upper mold members. He may then operate the start button 112 when he is ready to shift the table 15 to a new position which places `another llower mold member at an ejecting station.

It is Itherefore seen that the invention provides a molded article ejecting mechanism which is versatile and capable of accurate control. The ejection effected thereby is positive. The height of ejection and the depth of retraction Imay be suitably selected by positioning the nuts 93 and 94 on the rod 91. The gauge 100 adjacent the rod 91 provides a convenient indication of the extent of movement of the knock-out pins 60 and 61.

The arrangement of the pins 60 and 61 operating through the openings 65 provides versatility in the selection and configuration of lower mold members. Such mold members may include as many ejecting pins 55 on the stripper plate 58 as are convenient or desirable for the eicient ejection of the molded article. Also, the top and bottom mold sub-shoes 41 and 46 may be replaced at the conclusion of a given run or, if necessary, the entire mold shoes may be replaced with substitute shoes which are compatible for Iuse with the knock-out pins 60 and 61.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is dened in the appended claims.

What is claimed is: v

`1. In a plastic injection machine including a bed and a table guide on said bed with a shiftable table on said guide supporting a pair of spaced apart lower mold members for respective movement between a central injecting station and opposite ejecting stations adjacent the ends of said table guide, the improvement comprising knockout pin supporting means at each of said ejecting stations positioned beneath said bed, upwardly extending knockout pins for each of said ejecting stations supported at their lower ends directly to said pin supporting means, means in said guide and said bed at each of said ejecting stations defining openings supporting a substantial portion of the length of said pins for guided raising and lowering stripping movement therein with the upper ends of said pins received and supported in said table guide openings beneath said table in the lowered position thereof, means in said table defining openings beneath said lower mold members providing for the movement of the upper ends of said pins therethrough, said pins being proportioned to extend into operative engagement with said lower mold members through said table openings in the raised position thereof, a knock-out pin operating motor for each of said stations including a hydraulic piston motor having a fixed cylinder and a piston rod connected to said knock-out pin supporting means to eiect said guided ejecting movement of said pins in said bed and table guide, a source of hydraulic iluid Iunder pressure, a separate electric control valve for each of said motors, and a common control circuit for said valves including a first pair of limit switches for actuation in response to movement of said table linto said ejection stations for the respective selection of said control valves to effect the ejection of a molded article from one of said lower mold members at the associated said station, a second pair of limit switches, one for each of said ejecting stations, having contacts connected to control the associated said control valve and positioned to be operated in response to the ejecting movement of said piston rod to limit the extent of raising movement thereof, and a function selector switch in said circuit having a pair of selectable positions with contacts in the iirst of said selectable positions connected through said second pair of limit switches to provide for the raising and holding of said pins in a raised ejecting position and having further contacts in the second of said selectable positions providing for the raising followed immediately by the lowering of said knock-out pins.

2. In a plastic injection machine including a bed, a movable table on said bed supporting a pair of spaced apart lower mold members carried thereon for respective movement into ejecting stations at opposite ends of said table, the improvement comprising knock-out pins at each of said stations reciprocably mounted in said bed and movable between a lowered position clear of said table and a raised position, means in said table providing for movement of the upper ends of said pins into said raised position with said pins being proportioned to extend through said table and into engagement with said lower mold members, knock-out pin operating means for each of said stations inclu-ding a 2-way hydraulic piston motor having a cylinder mounted on said bed and an extensible piston rod connected to elect said raising and lowering of the associated said knock-out pins at said stations, hydraulic motor operating means including a source of 7 hydraulic fluid under pressure, a separate three-position, self-centering solenoid operatedcontrol valve for each of said motors, each of said valves being connected to said source of hydraulic pressure and having a dead center position and opposite electrically selectable ow reversing positions, each of said valves being connected to one of said hydraulic motors to block movement thereof in said center position and to apply hydraulic pressure thereto selectively to effect raising and lowering thereof in said opposite selectable positions, and a control circuit for said valves including a rst pair of limit switches for actuation in response to movement of said table into said ejecting stations for the respective selection of said control valves to eir'ect the ejection of a molded article from the one of the mold members which is in an ejection station, a second pair of limit switches, one for each of Vsaid stations having contacts connected to control the associated said control valve and positioned to be operated lin response to the ejection movement of said .piston rod to limit the extent of upward movement thereof, and a 3-way functon selector switch in said circuit having one position blocking lautomatic operation and a pair of'selectable positions with contacts 'in the rst of said References Cited in the file of this patent UNITED STATES PATENTS 1,871,406 DeTurk et al. Aug. 9, 1932 2,239,248 Rieser Apr, 22, 1941 2,289,102 Clark Iuly 7, 1942 2,298,044 Dinzl Oct. 6, 1942 2,410,510 Lester Nov. 5, 1946 2,465,889 Lester Mar. 29, y1949 2,582,891 Strauss Ian. 15, 1952 2,675,583 Scherry Apr. 20, 1954 2,757,414 Chaloupka Aug. 7, 1956 2,839,786 Alesi June 24, 1958 FOREIGN PATENTS 552.020 Great Britain Mar. 19. 1943 

1. IN A PLASTIC INJECTION MACHINE INCLUDING A BED AND A TABLE GUIDE ON SAID BED WITH A SHIFTABLE TABLE ON SAID GUIDE SUPPORTING A PAIR OF SPACED APART LOWER MOLD MEMBERS FOR RESPECTIVE MOVEMENT BETWEEN A CENTRAL INJECTING STATION AND OPPOSITE EJECTING STATIONS ADJACENT THE ENDS OF SAID TABLE GUIDE, THE IMPROVEMENT COMPRISING KNOCKOUT PIN SUPPORTING MEANS AT EACH OF SAID EJECTING STATIONS POSITIONED BENEATH SAID BED, UPWARDLY EXTENDING KNOCKOUT PINS FOR EACH OF SAID EJECTING STATIONS SUPPORTED AT THEIR LOWER ENDS DIRECTLY TO SAID PIN SUPPORTING MEANS, MEANS IN SAID GUIDE AND SAID BED AT EACH OF SAID EJECTING STATIONS DEFINING OPENINGS SUPPORTING A SUBSTANTIAL PORTION OF THE LENGTH OF SAID PINS FOR GUIDE RAISING AND LOWERING STRIPPING MOVEMENT THEREIN WITH THE UPPER ENDS OF SAID PINS RECEIVED AND SUPPORTED IN SAID TABLE GUIDE OPENINGS BENEATH SAID TABLE IN THE LOWERED POSITION THEREOF, MEANS IN SAID TABLE DEFINING OPENINGS BENEATH SAID LOWER MOLD MEMBERS PROVIDING FOR THE MOVEMENT OF THE UPPER ENDS OF SAID PINS THERETHROUGH, SAID PINS BEING PROPORTIONED TO EXTEND INTO OPERATIVE ENGAGEMENT WITH SAID LOWER MOLD MEMBERS THROUGH SAID TABLE OPENINGS IN THE RAISED POSITION THEREOF, A KNOCK-OUT PIN OPERATING MOTOR FOR EACH OF SAID STATIONS INCLUDING A HYDRAULIC PISTON MOTOR HAVING A FIXED CYLINDER AND A PISTON ROD CONNECTED TO SAID KNOCK-OUT PIN SUPPORTING MEANS TO EFFECT SAID GUIDED EJECTING MOVEMENT OF SAID PINS IN SAID BED AND TABLE GUIDE, A SOURCE OF HYDRAULIC FLUID UNDER PRESSURE, A SEPARATE ELECTRIC CONTROL VALVE FOR EACH OF SAID MOTORS, AND A COMMON CONTROL CIRCUIT FOR SAID VALVES INCLUDING A FIRST PAIR OF LIMIT SWITCHES FOR ACTUATION IN RESPONSE TO MOVEMENT OF SAID TABLE INTO SAID EJECTION STATIONS FOR THE RESPECTIVE SELECTION OF SAID CONTROL VALVES TO EFFECT THE EJECTION OF MOLDED ARTICLE FROM ONE OF SAID LOWER MOLD MEMBERS AT THE ASSOCIATED SAID STATION, A SECOND PAIR OF LIMIT SWITCHES, ONE FOR EACH OF SAID EJECTING STATIONS, HAVING CONTACT CONNECTED TO CONTROL THE ASSOCIATED SAID CONTROL VALVE AND POSITIONED TO BE OPERATED IN RESPONSE TO THE EJECTING MOVEMENT OF SAID PISTON ROD TO LIMIT THE EXTENT OF RAISING MOVEMENT THEREOF, AND A FUNCTION SELECTOR SWITCH IN SAID CIRCUIT HAVING A PAIR OF SELECTABLE POSITIONS WITH CONTACTS IN THE FIRST OF SAID SELECTABLE POSITIONS CONNECTED THROUGH SAID SECOND PAIR OF LIMIT SWITCHES TO PROVIDE FOR THE RAISING AND HOLDING OF SAID PINS IN A RAISED EJECTING POSITION AND HAVING FURTHER CONTACTS IN THE SECOND OF SAID SELECTABLE POSITIONS PROVIDING FOR THE RAISING FOLLOWED IMMEDIATELY BY THE LOWERING OF SAID KNOCK-OUT PINS. 